Belt drives are commonly used to transmit power from a drive pulley to one or more driven pulleys. One problem encountered in belt drives is the maintenance of proper belt tension. Insufficient belt tension allows the belt to slip on the drive and/or driven pulleys and such belt slippage not only reduces the power transmitted from the drive to the driven pulleys, but also produces noise and heat which can cause hardening and deterioration of the belt. Excessive belt tension, on the other hand produces excessive bearing loads on the various devices connected by the belt drive and further tends to cause stretching of the belt. Another problem encountered in belt drives, particularly those utilized for driving a plurality of accessories on an internal combustion engine, is that the belt tends to vibrate, particularly under non-uniform or pulsating loads such as those encountered when certain accessories such as the air conditioner are being driven.
Various different belt tensioning devices such as shown in U.S. Pat. Nos. 1,557,486; 2,663,195; 3,374,686 and 4,145,934 have heretofore been proposed to maintain a more uniform tension on the belt. In general, such belt tensioning devices include an idler pulley which is mounted on an arm yieldably biased in a direction to tension the belt. The belt tensioning device in U.S. Pat. Nos. 1,557,486, 2,663,195 and 3,374,686 mount the arm or lever of the belt tensioning device so that it can move both inwardly and outwardly relative to the belt to control belt tension. However, the belt tensioning devices of those patents have no provision for controlling vibration or oscillation of the belt tensioning device and belt. U.S. Pat. No. 4,145,934 provides a wedge on the lever arm of the belt tensioner that engages an eccentric cam on the lever arm pivot to provide an adjustable stop which allows the belt tensioning pulley to move inwardly toward the belt when the belt tension decreases, but which inhibits outward movement of the pulley and lever arm in the event the belt tension increases. Although the patent states that the wedge member can be formed of an elastomeric material for added dampening, a wedge member of elastomeric material would only function as a resilient abutment or stop to limit movement of the belt tensioning device in a direction outwardly of the belt.